1. Field of the Invention
The present invention relates to an egg freezing and storing instrument used to freeze and store eggs such as ova and mammalian embryos and a method to be carried out in using the egg freezing and storing instrument.
2. Description of the Related Art
Freezing and storing the mammalian embryo enables conservation of hereditary resources of specific systems and kinds, is effective for maintaining animals standing on the brink of ruin, and is useful for coping with sterility.
As disclosed in Japanese Patent Application Laid-Open No. 2000-189155 (patent document 1), there is proposed a method for freezing and storing mammalian embryos. In this method, mammalian embryos or ova are bonded to the inner surface of the freezing and storing container such as the sterilized frozen straw, frozen vial or frozen tube by using a vitrified liquid in an amount minimum and enough to enclose the mammalian embryos or the ova therewith. The freezing and storing container is sealed and rapidly cooled by bringing the freezing and storing container into contact with liquid nitrogen. In the thawing method of this proposal, the freezing and storing container stored in the above method is taken out of the liquid nitrogen and one end thereof is opened. A diluted liquid of 33 to 39° C. is injected directly into the container to thaw the mammalian embryos or the ova and dilute the vitrified liquid. This method eliminates a possibility that the mammalian embryos or the ova are infected with a disease through viruses or bacteria and is capable of storing them at a high survival rate and thawing them and diluting the vitrified liquid.
The present applicant proposed the egg freezing and storing instrument, as disclosed in Japanese Patent Application Laid-Open No. 2002-315573 (patent document 2). The egg freezing and storing instrument includes the body part made of a cold-proof material; the strip, made of a material flexible, transparent, and resistant to liquid nitrogen, mounted at one end of the body part to hold eggs attached thereto; and the cylindrical member which is made of a cold-proof material and whose one end is sealed. The cylindrical member allows the egg-holding strip to be endosably mounted on the body part.
As disclosed in Japanese Patent Application Laid-Open No. 2001-252293 (patent document 3), there is proposed a tool for vitrifying eggs or embryos. The vitrifying tool has the cylindrical super-fine tubular part; and the connection part, continuous with the super-fine tubular part, to be mounted on the sucking and discharging tool. The minimum distance between the opposed two points on the inner surface, of the super-fine tubular part, vertical to the longitudinal direction thereof is shorter than the double of the minimum outer diameter of one ovum or one embryo and longer than the maximum diameter thereof. Therefore two or more ova or embryos are incapable of being present side by side on the inner surface of the super-fine tubular part vertical to the longitudinal direction thereof.
The method of the patent document 1 is effective for storing embryos or ova, but there is a demand for development of a freezing and storing instrument that can be operated easily.
The egg freezing and storing instrument of the patent document 2 has an advantage of collecting eggs very easily, but causes the eggs to contact the liquid nitrogen directly. Thus the egg freezing and storing instrument has a problem that the eggs are adversely affected by the liquid nitrogen.
The vitrifying tool of the patent document 3 has the effect that ova or embryos can be cooled rapidly because the ova or the embryos are collected and cooled inside the super-fine tubular part. However, there is a possibility that bacteria enter the vitrifying tool when a pipette which has collected the ova or the embryos from the vitrifying tool is separated therefrom. The vitrifying tool has another problem that the super-fine tubular part may be damaged in immersing the vitrifying tool in the liquid nitrogen. Another problem of the vitrifying tool is that it is necessary to perform a difficult work because the super-fine tubular part is required to be inserted into a storing outer cylinder in the presence of the liquid nitrogen.
Therefore it is an object of the present invention to provide an egg freezing and storing instrument and method capable of preventing permeation of bacteria into a tube of the tool, while an operation of freezing (vitrifying) and storing an egg in a liquid nitrogen tank is being performed; cooling the egg rapidly without bringing the egg into direct contact with liquid nitrogen, and keeping the egg in a stable state in the liquid nitrogen tank.